SPAD detectors are utilized in a variety of applications, such as low-light detection applications, time-of-flight (TOF) applications, and time-correlated single photon counting applications. A SPAD detector typically includes an array of SPAD pixels, with each SPAD pixel including a SPAD and related biasing and/or readout circuitry. Each SPAD includes a photosensitive region that is configured to detect low levels of light (down to a single photon) and to generate a corresponding output signal at the arrival times of the photons. When the light comprises photons of an emitted light pulse that are reflected from an object, the output signal can be used to estimate the arrival times of the photons at the SPAD detector after emission of the light pulse. The arrival times determine a times-of-flight for the photons. Multiple such times-of-flight can be used to estimate a distance to the object.
Under certain conditions, it is desirable to maximize the signal-to-noise ratios (SNR) of the SPADs in a SPAD detector. Such conditions include when a target that has a low reflectivity, an environment where a target is distant from the SPAD detector, or an environment with low lighting (e.g., dusk or night). In some instances, multiple SPADs (e.g., two to three SPADs) may be sensing simultaneously and the signals binned to improve the SNR. However, binning the signals reduces the spatial resolution of the SPAD detector.